The continuous increase of data-traffic demand challenges and drives the mobile telecommunication industry to introduce new frequency bands, standards and radio access technologies e.g. MIMO, beamforming etc. From an antenna point of view that means multiple antenna systems which offer more agile beam possibilities. In order to achieve more agile beam antennas, phase and amplitude have to be set in real time and in a flexible way. This leads to so called Active Antenna Systems, AAS, which means integrating radio transceiver units, RRU, with base station antenna systems. This integration leads to highly complex systems and strongly influences the antenna form factor which is fundamental for commercial field deployment. Replacing traditional antennas with AAS or simply obtaining new site permissions if the form factor of the antenna is not similar to traditional antennas is a time consuming and hard task to be fulfilled for the operators, and this is also valid for traditional passive base station antenna systems.
As it is well known, ultra broad band base station antenna systems typically operate in the 698-960 MHz (“Low Band”) and 1.7-2.7 GHz (“High Band”) spectrum which includes most cellular network frequency bands used today. A relative bandwidth of the ultra broad band base station antenna systems can be calculated by the equation:The relative bandwidth=2*(fmax−fmin)/(fmax+fmin),
and is supposed to be greater than 30%.
On the one hand, a base station antenna element must have a sufficient depth for supporting the lowest frequency of the cellular network frequency bands and achieving a relative bandwidth which is greater than 30%. In the meanwhile, with the growing demand for a deeper integration of antennas with Radios, as e.g. in AAS, it is very important to reduce the dimensions of ultra broad band antennas without compromising the antenna's key performance.
In view of the above, one of the dominant limiting technological factors for reducing the overall antenna dimensions is the height of the lower band radiating element which strongly influences the overall antenna depth. Significantly reducing the antenna height means to strongly simplify the overall deploying process of AAS and traditional passive antenna systems.
Conventional base station antennas, do not present any solutions for reducing the lower frequency antenna element depth during supporting the lowest frequency of the cellular network frequency bands and achieving a relative bandwidth which is greater than 30%.